Fluid ejection heads for fluid ejection devices such as ink jet printers, vapor evaporation devices, and the like continue to be improved as the technology for making the ejection heads continues to advance. New techniques are constantly being developed to provide low cost, highly reliable fluid ejection head structures that can be manufactured in high yield with a relatively low amount of spoilage or ejection head damage.
In order to increase ejection head speed and volume output, larger ejection heads having an increased number of ejection actuators are being developed. However, as the ejection head size and number of ejection actuators increases, manufacturing apparatus and techniques are required to meet increased tolerance demands for such ejection heads. Slight variations in tolerances of parts may have a significant impact on the operation and yield of suitable ejection head products.
The primary components of the fluid ejection head are a chip or chip containing fluid ejector actuators, and a nozzle plate attached to the chip. The chip is typically made of silicon and contains various passivation layers, conductive metal layers, resistive layers, insulative layers and protective layers deposited on a device surface thereof. For thermal fluid ejection heads, individual heaters are defined in the resistive layers and each heater resistor corresponds to a nozzle hole in the nozzle plate for heating and ejecting fluid from the ejection head toward a target media. Fluid ejection heads may also include bubble pump type ejection head. In a top-shooter type ejection head, nozzle plates are attached to the chips and there are fluid chambers and fluid feed channels for directing fluid to each of the heaters or bubble pumps on the chip either formed in the nozzle plate material or in a separate thick film layer. In a center feed design for a top-shooter type ejection head, fluid is supplied to the channels and chambers from a slot or via that is conventionally formed by chemically etching or grit blasting through the thickness of the chip. The chip containing the nozzle plate is typically bonded to a thermoplastic body using a heat curable adhesive to provide a fluid ejection head structure.
The thermal cure process locks the components together at an elevated temperature. The heater chip has a relatively low coefficient of thermal expansion (CTE) while the plastic body has a relatively high CTE. Heating the components causes each one to expand according to their respective CTEs. As the parts cool and shrink, the higher CTE plastic body shrinks more than the lower CTE silicon heater chip resulting in thermal stresses on the chip. The force-deflection (spring rate) characteristics of the chip and body determine the equilibrium deflection of each part.
In order to address the issues related to thermal compression of the chip as the chip and plastic body cool, ceramic substrates have been attached to the chip. However, ceramic substrates substantially increase the cost of the ejection head. Silicon bridges in a via area of the chip have also been used, but such silicon bridges result in fluid flow problems in the chip via area.
It is believed that a predominant contributor of chip distortion and cracking is the coefficient of thermal expansion mismatch between the chip and the thermoplastic body. During manufacturing, when the chip and body go through the adhesive cure cycle, chip distortion is introduced as the components cool. Accordingly, there continues to be a need for improved manufacturing processes and techniques which provide improved ejection head components and structures without product loss due to chip cracking.
With regard to the above, there is provided a fluid ejection head having a fluid supply body having a nosepiece with at least one fluid supply port formed therein. A pedestal extends outwards from an exterior surface of the nosepiece proximate the at least one fluid supply port. The pedestal has a perimeter edge that, in some cases is dog-bone shaped. A semiconductor chip mounting surface is formed within the perimeter edge.
A flexible circuit bonding surface also extends outwards from the exterior surface of the nosepiece adjacent the perimeter edge of the pedestal. In certain cases, the pedestal has opposing side surfaces and opposing end surfaces and the flexible circuit bonding surface is adjacent each of the side and end surfaces of the pedestal. In other cases, the flexible circuit bonding surface may be located along only the sides of the pedestal.
A damage reducing structure is located between the perimeter edge of the pedestal and the flexible circuit bonding surface for reducing damage to a semiconductor chip mounted on the pedestal. In certain cases, the damage reducing structure is a void space. The void space isolates the pedestal from the surrounding flexible circuit bonding surface such that damaging shocks acting on the fluid supply body, such as those caused by drops, are reduced or eliminated prior to reaching the flexible circuit bonding surface and the chip that is mounted thereon. In other cases, the damage reducing structure may be a corrosion resistant compressible member, such as a silicone rubber.
In certain embodiments, the flexible circuit bonding surface includes a plurality of ribs. Preferably, the ribs (or a portion thereof) have a substantially planar top surface that is suitable for forming the flexible circuit bonding surface.
The length and thickness of the ribs may be varied as required to improve the isolation of the pedestal from the surrounding flexible circuit bonding surface but, at the same time, to provide for sufficient structural support for the chip and the fluid supply body in general. In certain embodiments, a mix of ribs including ribs having a first length and ribs having a second length may be used. For example, in certain embodiments, the pedestal has opposing side surfaces and opposing end surfaces and at least three ribs are located adjacent each side and at least two ribs are located adjacent each end of the pedestal. Additionally, the ribs may be oriented at different angles with respect to other ribs. For example, the fluid supply body may include a first rib and a second rib that is oriented at an angle Θ with respect to the first rib. The angle Θ may vary and, in certain cases, is greater than 0° and less than 180°. In other cases, Θ is greater than 45° and less than 135°.
Preferably, the ribs extending towards the pedestal do not contact the pedestal in order to maintain the isolation of the pedestal form the flexible circuit bonding surface. There is a damage reducing structure located between each adjacent pair of the plurality of ribs. In certain cases, the damage reducing structure is a void space. In other cases, the damage reducing structure may be a corrosion resistant compressible member, such as a silicone rubber.